Animals are multicellular, multifllular organisms in the Kingdom Animalia. With few exceptions, all animals eat organic matter, breathe air, can move, can reproduction sexually, and can be subjected to psychological stresses that cause behavior. Most behavior is carried out by the nervous system. The term “animal” refers to any of the following classes: mammals, amphibians, reptiles, crustaceans, birds, fish, mollusks, ungulates, primates, insectivores, birds-and mammals together with some forms of plants. Humans belong to the class Prototheria.
The major groupings of animals into which we today lump the various species of the animal kingdom are categorized on the basis of their physiology and anatomy. Primates are those animals whose anatomy is broadly similar to all other mammals. Multituberculates are those animals with a spinal chord or cervical vertebra, but no limbs. amphibians are those having both a tail and a torso, but no legs. Circumpolar are those animals with a soft body and an egg-laying uterus. Metatheria are those with bony armor plating on the external parts of the body.
The crux of the issue of animal rights and animal experimentation relates to the use of animals in medical research and experimentation. All animals are considered to be subjects of research unless specifically exempted. Although it has been customary in some cultures since the time of the ancient Egyptian pharaohs to experiment on animals, such experimenting has been prohibited since the Humane Society campaign began in 1900. While the United States and the European Union are the only places in the world to have legal protections in place for animal rights, the practice still largely exists in industrialized nations like China, India, and Malaysia. There is very little documentation of animal experiments, except in the case of animal breeding and experimentation, in most other cases the only visual records that exist are poorly written, dated, or just not there.
For example, if you look at any zoo today, you will see a variety of mammals, amphibians, reptiles, insects, etc. where the only requirement is that they be de-clawed, which can obviously occur because of the methods used to restrain them. Another common practice is to breed dogs and cats using certain creatures as their only reproduce, such as monkeys and rats. This has led to the mass breeding of these animals where they suffer from serious health issues. For example, millions of tigers, monkeys, and various other big cats are killed every year because of diseases caused by unsterile breeding methods.
On the other hand, there are some examples where sexual reproduction between animals is allowed. This is because the sexual behaviors and the ability to reproduce are generally useful for both the species involved, although the purpose of sexual reproduction might differ between different species. Some birds actually mate by mating for life, which is why you sometimes see a nest of one bird with a number of eggs, whereas on another occasion you might see two birds laying eggs but no reproductive adult to keep them together. Many animals actually have a way of producing both asexually by either engaging in sexual behavior or the presence of females and males of the same species. These are the examples where sexual reproduction has been allowed between organisms.
Sexual reproduction between animals can be a normal part of their development, although there are some animals that do not do this. The best example of an animal that engages in e.g. in sexual reproduction is the octopus. While it is normal for the octopus to engage in sexual reproduction through the union of its partners, when that occurs, the octopus is considered a sexually abnormal creature since it actually carries the gene that causes it to reproduce.